API Patterns Skill

Purpose

Design and implement APIs using the optimal pattern and framework for the use case. Choose between REST, GraphQL, gRPC, and tRPC based on API consumers, performance requirements, and type safety needs.

When to Use This Skill

Use when:

• Building backend APIs for web, mobile, or service consumers
• Connecting frontend components (forms, tables, dashboards) to databases
• Implementing pagination, rate limiting, or caching strategies
• Generating OpenAPI documentation automatically
• Choosing between REST, GraphQL, gRPC, or tRPC patterns
• Integrating authentication and authorization
• Optimizing API performance and scalability

Quick Decision Framework

WHO CONSUMES YOUR API?
├─ PUBLIC/THIRD-PARTY DEVELOPERS → REST with OpenAPI
│  ├─ Python → FastAPI (auto-docs, 40k req/s)
│  ├─ TypeScript → Hono (edge-first, 50k req/s, 14KB)
│  ├─ Rust → Axum (140k req/s, <1ms latency)
│  └─ Go → Gin (100k+ req/s, mature ecosystem)
│
├─ FRONTEND TEAM (same org)
│  ├─ TypeScript full-stack? → tRPC (E2E type safety)
│  └─ Complex data needs? → GraphQL
│      ├─ Python → Strawberry
│      ├─ Rust → async-graphql
│      ├─ Go → gqlgen
│      └─ TypeScript → Pothos
│
├─ SERVICE-TO-SERVICE (microservices)
│  └─ High performance → gRPC
│      ├─ Rust → Tonic
│      ├─ Go → Connect-Go (browser-friendly)
│      └─ Python → grpcio
│
└─ MOBILE APPS
   ├─ Bandwidth constrained → GraphQL (request only needed fields)
   └─ Simple CRUD → REST (standard, well-understood)

REST Framework Selection

Python: FastAPI (Recommended)

Key Features: Auto OpenAPI docs, Pydantic v2 validation, async/await, 40k req/s

Basic Example:

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Item(BaseModel):
    name: str
    price: float

@app.post("/items")
async def create_item(item: Item):
    return {"id": 1, **item.dict()}

See references/rest-design-principles.md for FastAPI patterns and examples/python-fastapi/.

TypeScript: Hono (Edge-First)

Key Features: 14KB bundle, runs on any runtime (Node/Deno/Bun/edge), Zod validation, 50k req/s

Basic Example:

import { Hono } from 'hono'
import { zValidator } from '@hono/zod-validator'
import { z } from 'zod'

const app = new Hono()
app.post('/items', zValidator('json', z.object({
  name: z.string(), price: z.number()
})), (c) => c.json({ id: 1, ...c.req.valid('json') }))

See references/rest-design-principles.md for Hono patterns and examples/typescript-hono/.

TypeScript: tRPC (Full-Stack Type Safety)

Key Features: Zero codegen, E2E type safety, React Query integration, WebSocket subscriptions

Basic Example:

import { initTRPC } from '@trpc/server'
import { z } from 'zod'

const t = initTRPC.create()
export const appRouter = t.router({
  createItem: t.procedure
    .input(z.object({ name: z.string(), price: z.number() }))
    .mutation(({ input }) => ({ id: '1', ...input }))
})
export type AppRouter = typeof appRouter

See references/trpc-setup-guide.md for setup patterns and examples/typescript-trpc/.

Rust: Axum (High Performance)

Key Features: Tower middleware, type-safe extractors, 140k req/s, compile-time verification

Basic Example:

use axum::{routing::post, Json, Router};
use serde::{Deserialize, Serialize};

#[derive(Deserialize)]
struct CreateItem { name: String, price: f64 }

#[derive(Serialize)]
struct Item { id: u64, name: String, price: f64 }

async fn create_item(Json(payload): Json<CreateItem>) -> Json<Item> {
    Json(Item { id: 1, name: payload.name, price: payload.price })
}

See references/rest-design-principles.md for Axum patterns and examples/rust-axum/.

Go: Gin (Mature Ecosystem)

Key Features: Largest Go ecosystem, 100k+ req/s, struct tag validation

Basic Example:

type Item struct {
    Name  string  `json:"name" binding:"required"`
    Price float64 `json:"price" binding:"required,gt=0"`
}

r := gin.Default()
r.POST("/items", func(c *gin.Context) {
    var item Item
    if c.ShouldBindJSON(&item); err != nil {
        c.JSON(400, gin.H{"error": err.Error()}); return
    }
    c.JSON(201, item)
})

See references/rest-design-principles.md for Gin patterns and examples/go-gin/.

Performance Benchmarks

Notes:

• Benchmarks assume single-core, JSON responses
• Actual performance varies with workload complexity
• Cold start only applies to serverless/edge deployments

Pagination Strategies

Cursor-Based (Recommended)

Advantages: Handles real-time changes, no skipped/duplicate records, scales to billions

FastAPI Example:

@app.get("/items")
async def list_items(cursor: Optional[str] = None, limit: int = 20):
    query = db.query(Item).filter(Item.id > cursor) if cursor else db.query(Item)
    items = query.limit(limit).all()
    return {
        "items": items,
        "next_cursor": items[-1].id if items else None,
        "has_more": len(items) == limit
    }

Offset-Based (Simple Cases Only)

Use only for static datasets (<10k records) with direct page access needs.

See references/pagination-patterns.md for complete patterns and frontend integration.

OpenAPI Documentation

FastAPI Example (Zero Config):

app = FastAPI(title="My API", version="1.0.0")

@app.post("/items", tags=["items"])
async def create_item(item: Item) -> Item:
    """Create item with name and price"""
    return item
# Docs at /docs, /redoc, /openapi.json

See references/openapi-documentation.md for framework-specific setup. Use scripts/generate_openapi.py to extract specs programmatically.

Frontend Integration Patterns

Forms → REST POST/PUT

Backend:

class UserCreate(BaseModel):
    email: EmailStr; name: str; age: int

@app.post("/api/users", status_code=201)
async def create_user(user: UserCreate):
    return {"id": 1, **user.dict()}

Frontend:

const res = await fetch('/api/users', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify(data)
})
if (!res.ok) throw new Error((await res.json()).detail)

Tables → GET with Pagination

See cursor pagination example above and references/pagination-patterns.md.

AI Chat → SSE Streaming

Backend:

from sse_starlette.sse import EventSourceResponse

@app.post("/api/chat")
async def chat(message: str):
    async def gen():
        for chunk in llm_stream(message):
            yield {"event": "message", "data": chunk}
    return EventSourceResponse(gen())

Frontend:

const es = new EventSource('/api/chat')
es.addEventListener('message', (e) => appendToChat(e.data))

See examples/ for complete integration examples with each frontend skill.

Rate Limiting

FastAPI Example (Token Bucket):

from slowapi import Limiter
from slowapi.util import get_remote_address

limiter = Limiter(key_func=get_remote_address)
app.state.limiter = limiter

@app.get("/items